Retrieval devices are often used to remove organic material (e.g., blood clots, tissue, and biological concretions such as urinary, biliary, and pancreatic stones) and inorganic material (e.g., components of a medical device or other foreign matter), which may obstruct or otherwise be present within a patient's body cavities or passages. For example, concretions can develop in certain parts of the body, such as in the kidneys, pancreas, ureter, and gallbladder. Minimally invasive medical procedures are used to remove these concretions through natural orifices, or through an incision, such as during a percutaneous nephrolithotomy (“PCNL”) procedure. Further, lithotripsy and ureteroscopy, for example, are used to treat urinary calculi (e.g., kidney stones) in the ureter of a patient.
Retrieval devices may include end effectors for manipulating objects. An exemplary end effector may have a plurality of arms that support a front loop that forms when the end effector is opened. The size of the front loop may limit the size of an object that can be captured, repositioned, and/or released from the end effector. For some procedures, there may be a need to increase the size of a front loop of an end effector to facilitate the capturing, repositioning, and/or releasing of larger objects. It may also be desirable to have an end effector close back down to a low-profile state to facilitate insertion and withdrawal of the end effector into and from a target area, and/or to capture, reposition, and/or release smaller objects. Thus, there remains a need for retrieval devices with improved capabilities.
Further, known medical retrieval devices are complex, requiring many components and labor-intensive manufacturing processes. The assembly of small parts often requires visual magnification and specialized training. The available joining mechanisms often increase the profile of the medical retrieval devices beyond optimal design parameters, and are often the weakest structural points. These drawbacks result in medical retrieval devices that are bulky, expensive, and prone to failure.
Further, it is often desirable to measure the diameter of kidney stones or stone fragments before, during, or after removal from the patient. This measurement helps the urologist determine how to treat the stone and how to counsel the patient after completion of the procedure. Currently, urologists roughly estimate the diameter of a stone or fragment by visually comparing a reference object of known size (e.g., a retrieval device or guidewire diameter) to the stone under direct endoscopic visualization. This technique results in widely varying and often inaccurate estimates of stone size.
Thus, there remains a need for improved medical retrieval devices having reduced profiles and fewer components, and for improved mechanisms for determining the size of a stone in vivo.